US2531508A - Color television system - Google Patents

Description

Nov. 28,1950 A. N. GOLDSMITH 2,531,508

COLOR TELEVISION SYSTEM Filed July 30, 1946 2 Sheets-Sheet 1 AMPLIFIER L TRANSMITTER BIAS CONTROL AMPLIFIER F 4/ 5/45 M CONTROL AMPLIFIER 1 i J r r FIELD FREQUENCY AMPLIFIER GENERATOR ,45 47 MUN/FIELD r V FREQUENCY AMPUF/ER GENERATOR LINE FREQUENCY AMPLIFIER 4 am-mro/z MULT/ LINE INVENTOR FREQUENCY AMPLIFIER GENERATOR BY ALFRED N. GOLDSMITH ATTORN EY Nov. 28, 1950 Filed July 30, 1946 A. N. GOLDSMITH COLOR TELEVISION SYSTEM 2 Sheets-Sheet 2 INVENTOR ALFRED N. GOLDBMITH BY f ATTORNEY fiatented Nov. 28,

invites stares PATENT other some TELEVISION rant 18 Claims.

This invention relates to television systems and more particularly to the systematic removal of any residual image or electrical non-uniformity on the photo-sensitive surface of an iconoscope, orthicon, or an analogous camera tube.

The principle of big t storage employed in the iconoscope involves setting up a flat plate termed the photo-sensitive mosaic, the surface of which is illuminated through a lens by the scene to be transmitted, the image of which is focussed upon the mosaic. The flat surface contains a coating of globules oi insulated photo-sensitive material. The photo-sensitivity characteristic is employed to release electrons from the surface in the form of an electron image. The electron image is not utilized directly, but is allowed todissipate itself within the tube, the electrons being col lected by an electrode and removed from the tube without further use.

The insulation characteristic of the surfaceis employed to preserve the configuration of the charge deficiency on the plate. This conservation of charge continues for as long as is required, and the value of the charge deficiency at any point on the surface continues. to increase the longer the light is allowed to fall upon it, though not necessarily uniformly. Consequently, the light is effectively stored in the form of stored charges, the distribution of which corresponds to that of the light in the scene to be transmitted.

When the electron scanning beam passes over a picture element, it makes use not only of the light which illuminates the element at that instant, but also of the light which has fallen on that element since the previous passage of the scanning beam.

Each globule in the mosaic surface of the icona much more rapid rate than that at which it' was charged. The sudden discharge acting through the capacitance to the signal coating appears as a current impulse in the signal circuit connected to the signal coating.

It might be assumed that no charge deficiency would be present on the mosaic and no signal would appear if the surface was scanned while 2 unilluminated. .It is found, however, that a signal does appear. The signal reflects the fact that certain parts of the mosaic have become charged at the expense of other parts. The unequal distribution of charge is explained by the fact that the scanning beam impinging on the globules of the mosaic frees secondary electrons from them by force of impact. These secondary electrons are in part collected by the nearby collector-anode which is maintained at a positive potential. However, since the mosaic is insulated, no more electrons can leave the plate than reach it, and in consequence, the secondary electrons not collected by the collector-anode find themselves attracted back toward the plate. The secondary electrons in falling back on the mosaic do so in a more or less distributed shower which is not uniform, however, owing to local irregularities in the secondary-emission ratio of the surface and diiferences in the distribution of potential arising from the collecting field. Consequently, the secondary electron shower deposits itself on the mosaic in irregular distribution. The scanning beam, in scanning this irregular distribution of charge, produces a spurious signal that in turn produces an uneven shading in the reproduced image in the receiver.

The shading or dark-spot effects described above are deleterious in cyclic or sequential multi-color television scanning where a succession of pictures are scanned through their re-. spectively related color filters, since they may give rise to false color values in certain portions of the image.

It will also be seen that, due to the storage characteristics of the mosaic plate, a moving subject would produce a blurred image if the time interval allowed for storage of the globules were not reduced to a minimum. By sweeping the charge from the mosaic during the blanking period between successive fields or scannings, the elimination of such a residual image. can be accomplished to alarge extent.

There is an additional type of residual picture, so to speak, which it is sometimes desired to eliminate. If interlaced scanning is used, and if only anodd-line scanning is carried out, a residual image (which may endure for quite an appreciable period) exists in the even-line spaces which are as yet unscanned. Thestrength of such a residual image is a complicated function of the type of image tube, the scanning beam current, thebeampotential, the sharpness of focus of the beam under various conditions, and the like; It issometimes undesirable that such an unscanned area shall hold a picture, and ac" cordingly the present invention becomes useful in the e.imination of such residual images. The present invention may thus be applied for the elimination of all residual images between successive scannings.

The primary object of this invention, accordingly, is'to provide an improved television system.

Another object of this invention is to eliminate any electrical non-uniformity or shading effect on the photo-sensitive surface of an iconoscope or similar tube whereby any prior scanning or variable tube condition may affect alater scanning, it being applicable to -moriochrorne television, color television, stereoscopic televisionor the like.

A further object of this invention in'oneof its preferred forms is to confine the period of residual image elimination to a desired valueand to equalize to a predetermined extent theperiod of illumination and electron image storage -of all portions of the image.

istill another object of this invention is the elimination of any residual image, whether covering the entire mosaic of an iconoscope or only the odd-line or-even-line positions in an interlaced scanning regime. W e I Other and incidental objects of the-invention will be apparent to those skilled in the art from a reading of the followingspecificationand an inspection of the accompanying drawing inwhich Figure 1 illustrates schematically apreferred form of this invention;

Figures 2a, 2b, 2c, and 2d show graphically the operation of a preferred form of this invention; and r Y W e Fig-ore 3 shows schematically an arrangement whereby image scanning in color television'is carried out in the shadow of a 'dark 'spoke in the v rotating filter disk or drum, this spoke following 'agrelatively narrow color filter section.

In order to present for each successive "scanning an electrically fresh anduniform mosaic to the scanning process, the mosaic can be swept clean electrically, so to speak, between successive scannings and duringjthe vertical re turn period between successive field scannings. During this return period, the electron beam of the'iconoscope, with suitable characteristics, must pass over every portion of the mosaic during what may be termed the image-release period. The preferred characteristics of v the scanning during the image-release period inclu'de'the following:

1. The intensity of the scanning beam during the image-release period shall be best suited to that purpose and, in general, greater than that used for the normal picture scanning. Such control or increase of intensity of the beam may be accomplished by a correctly timed changing of the iconoscope gun bias suitably to regulate the beam intensity. I

2. The beam-spot area during the image-release scanning may be altered to the most suitable value for that purpose which, in general, may be greater than that used for the picture scanning so as to create a more uniform coverage, even overlap, and averaging effect at the mosaic. This change in the beam-spot area may also be accomplished by changing correspondingly and at appropriate times, the bias on suitable members of the electron-gun'assembly.

3, In order that the successive image-release scannings shal1 be substantially identicalf it is desirable that the frequency-of the vertical and represent typical rays passing through lens I.

horizontal deflections durin the image-release period shall be a whole-number multiple of the corresponding normal picture-scanning deflection frequency. The vertical scanning frequency during the image-release period, in an illustrative example described in detail below, is eight times the vertical scanning or field frequency during the normal picture scanning period. It is preferred, as will be shown, that 1 sawtooth scanning waves shall exist during the image-release period, which would be the same as the brief falling portion of the normal sawtooth deflection wave for picture scanning. Alternatively any larger odd number of half sawtooth waves of the image-release period frequency shall exist during that period, which period, as stated, correvertical picture-scanning deflection frequency.

If the two ratios are to be the same, the sawtooth waves for the image-release scanning and 'for the picture-scanning respectively must be homologous and similar (that is, the ratio of the time required for the rising portion of the sawtooth wave to the time required for the falling-portion of the sawtooth wave shall be the same in both instances). It is preferable that the sawtooth waves shall in fact be homologous for the imagerelease scanning and the normal picture scanning Referring now in detail 'to Figure 1, objective lens I on optical axis 3 focuses a light image of external subjects on the mosaic 5 of the iconoscope or other suitable camera tube 1. 9 and H An electrode !3 controls the intensity of the electron beam I5 which is used for scanning the mosaic 5. Deflection plates I! and 19 are illustrated as purely representative and conventional means utilized to control the electron beam in the desired'scanning sequence. Electrode 21 provides a control for the focusing of electron beam I5.

The electrode 23 of the iconoscope Y has its usual function of removing secondary electrons, as well as an accelerating element. The signal plate 25 is used to withdraw the video signal to the amplifier Z1 and thence to the transmitter 29.

It will be seen that, by using the electron beam as a broom, the mosaic 5 may be swept free of charge during the image time or interval of time normally allotted to the return of the electron beam to the position from which it starts its scanning of the image.

The electron beam i5 may be broadened'during the image release time by applying a proper bias to the focusing control electrode2 Ffrom the field frequency generator 3!. A signal can also be derived from field frecuency generator 3! properly to control the intensity of the electron beam.

It is necessary that amplifier 2'! be'bloclre'd during the image release interval in order that any spurious signal obtained from iconoscope 1 during that interval will not be transmitted. This can be accomplishedby providingampliflerf'l wi h asutroilbias d ringtheim ee e aseii ne int ya lhe b ck glof mplifi 2 ,.ca also eac m lished by d riv ng a si nal bias 'f the field frequency generator 3| such that during the blanking period or image" release period amplifier 21 is blocked and the iconoscope 1 is effectively disconnected from the television transmitter29. l p "1 The type of biasing required for broadening the beam and blocking amplifier 2! must necessarily'be greatervin a negative direction during the falling period of the sawtooth wave derived from the field frequency generator 3|. This can be accomplished by providing the field frequency generator 3| with an outputcoil 33., Coil ,33 is coupled to bias control amplifier 35 through coil 31, which is so polarized that the output Signal from bias control amplifier 35 is greater in a negative direction during the falling period of the sawtooth wave generated by field frequency generator 3|;

It -follows that during the image release in-v terval a potential is derived from bias control amplifier 35 and applied to electrode 2| to broaden the electron beam.

During the same interval, a bias is derived from control amplifier 35 and applied to amplifier 2'! to cause it to become inoperative for that interval.

During the rising portion of the vertical scan ning wave from the generator. 3|, the deflection voltagepasses to theiainplifierlsii and thenceto deflection-plates. l9. During the imagezrelease interval, it is neoessary'to prevent-the signal generated by field frequency generator 3| from reaching the deflection plates it, so there is-also derived from bias control amplifier 35 a bias p tentia'l whichwill make amplifier Edinoperativ during the image release time interval.

Coil 4| is also coupled to coil 33 so that th voltage induced therein is opposite in-Lpolarit to thatinduced in coil 37. ii

During the image release time intervaL'a bias is obtained from. bias amplifier 23 and applied to intensity control electrode IE to increase the intensity of the beam during the image release time interval. 1

A multiple field-frequency generator 25 pro duces a sawtooth wave having a frequency which is a multiple of that of generator 3|. The izieth ods of producing a multiple frequency are well known in the art andnee'd not be here described. The output of generator 45 passes to amplifier 4'! and thence to deflection plates |9. However, amplifier 47 is biased from the output of bias control amplifier 43 to make it operative only during the image release time interval because, during the rising portion of the sawtooth vertical scanning wave from generator 35, amplifier -43 biases amplifier 4'! to cut-off. However, during the falling portion of the vertical scan-f ning wave from generator 3!, amplifier t3 activates or releases amplifier 31 and thus per mits the application of the output of the multifield-frequency generator :35 to vertical deflection plates |9.

The-arrangement illustrated thus has forits purpose the application to 'vertical deflection plates l of the normal picture scanning wave from generator 3| during the rising portion of that wave but the application of the multi-field frequency imagez-releasescanning wave from generato1x45 during the -;period when the normal scanning wave, from generator'tl is falling.

The line-frequency generator 5! produces an output which passes "through amplifier 53 to the horizontaldefiection plates I! in the usual fashion; during the rising portion of the vertical scanning wave producedby generator 3|, as a result ofthe bias obtainable from amplifier and applied to amplifier 53. However, durin the falling portion of the vertical scanning wave from generatortl, the output of the multi 'line-frequency, generato1g55, is passed through amplifier 53, to the horizontal defiectionplates I! as a result of the bias obtained from amplifier 43.

V Theoverall system'functions as follows: During the rising portion of the normal vertical scanning wave, f rom generator 3|, the beam intensity is normal for image scanningof the selected type, the focus of the beam has a sharpness suitedto such normal picture scanning, a normal vertical scanning wave is applied to the vertical deflection control, and a normal scanning wave is applied to the horizontal deflection control. Thus the-usual picture scanning proceedsnormally in all respects-during the rising portion of the scannil gwave from generator 3|. However; during the falling portion of the scanning wave from generator 3|, the beam intensity is altered to any value suitable for image release or elimination,

the focusing of the spot on the mosaic is correspondingly modified for the same purpose, and the vertical and horizontal defiectionsare multiplied in speedso that, at, least one expedited or speededwup complete scanning cycle takes place I during the falling portion of the vertical scanning wavefrom generator 3|. For the purpose of explanation, an example is given of 1 image release scanning cycles-taking place during the falling portion of the :vertical scanning wave-a relationship which, in general, appears preferable.

In; Figure 2a there is shown the normal vertical scanning wave such as is produced by generators-3|, 596| is the rising portion referred totaboverand 6 |.'63 is the falling or image release, interval.

Figure 2b shows the multi-field-frequency sawtooth wave such as may be generated by 45. It will be noticed. that in this illustration, this image-release scanning wave has a frequency ei ht times that of. the normal scanning frequency shown in Figure 2a and that 1 scanning cycles E5-6Tcorrespond to thefalling portion 51-433 of the scanning wave of Figure 2a. In Figure 2b, the scanning wave is homologous and similar to that in Figure 2a, but this is not a necessary condition. For purposes of illustration, the time occupied by portion 6|-63 is approximately 16% 0f the entire length of wave 59-63.

' It is obvious that by changing the ratios of the periods occupied by 6|'63 and 59-fi|, respec tively,v and by suitably changing the shape of wave shown in Figure 2!), any desired quantitative relationships for the scanning and blanking pe-' riods may be closely approximated .or reached.

In Figure 20, there are shown details of the normal or image scanning wave and of the imagerelease wave. The amplitude of the latter can be made slightly greater than that of'the'former in order that they may add up to the composite scanning wave for finite switching times, and as shown in Figure 2d. It is assumed, however, for the purpose of explanation that the electronic switching from the output of generator 3| to the output of generator 45 is substantially instantaneous. i Figure 2d shows the significant portion of the composite vertical scanning wave for both'picture scanning and image-release scanning. During the period up to 69, both vertical and horizontal deflection, beam intensity, and focus are normal for picture scanning in the iconoscope. During the period from 69 to H wherein the normal vertical scanning wave 13 would fall, the vertical scanning and the horizontal scanning are both of the multiple frequency suitable for residual-image elimination. And, as will be noted, a complete scanning cycle for image release, namely 69, 15, TI, TI is included within that period.

. The quantitative relationship between the multiefield-frequency used during the image-release period and the normal scanning frequency used during the picture-scanning period will now be taken up. It isfirst assumed that sawtooth scanning waves are used both for the multi-fieldfrequency generator and for the field-frequency generatorQand that these waves are homologous. That is, -the ratio of the timeduring which the wave rises to its peak from zero amplitude to the time during which it falls from the peak back to zero amplitude is substantially identical for the two waves. Absolute identity is not necessary, but a close approximation thereto is desirable. If the ratio of the rising period to the falling period in each wave is designated as k, and if the multi-field frequency is 172 times the field frequency, and if there are 11 complete multi-fieldfrequency cycles occurring during the time of the falling portion of the field-frequency wave (together'with and preceding by a single coinp'lete falling portion of the multi-field-frequency wave within that same period of the falling portion of the main field-frequency wave), then it can -be simply shown that:

k equals (mn-1) /n Thus if one completeimageerelease cycle is to be weed, and if Ic equals 9 (that is, the return period in the main field-frequency wave is one-tenth of the total cycle), then m equals 11, and the multi-field-frequency i 11 times that of the field frequency.

Similarly,.if:the return period were 15% of the total period for the field-frequency wave, and if three complete -image-release cycles (plus a falling portion thereof) are to be used during the falling portion of the main field-frequency wave, it is found that m equals 21 for the smallest integral ratio of the multi-field frequency to the field frequency.

Turning now to Figure 3, there is shown one form of mobile color filter and for purpose of explanation takes the'form of rectangular opaque sections BI and B3 in series with strips 85, 81, and 89 representative of the color filtering areas, being green, red, and blue, respectively. While such filter assemblies are usually of the rotating disk or drum or multi-segment type, the mobile filter unit illustrated in Figure3 is a longitudinal strip carrying color filter elements separated by opaque sections. In disk assemblies, the color filters will usually be sectorial in their shape, and the intervening paque spaces will similarly be sectorial, and are usually referred to as spokes.

The direction of motion of the filter strip is indicated by arrow :95.

The breaks SI and 93 are intended to indicate that the-length of the spoke areas is selected appropriately in consideration of the following discussion and that the drawing is not to scale.

The fa e of a ty ical storage camer tub in x mpl an im e orthi on, has an ima area 99. The ima e Orthicon is described in 8 detail by R. D/Kell and G. C. Sziklai in an article entitled Image Orthicon Camera in the RCA Review for March 1946, vol. VII, No. 1.

Filter strips 85, 81, and B9, in moving in the direction of the arrow 95, move vertically downward across the image area 99.

After the scanning operation of a particular image frame, for example, a blue frame, has been completed at a point corresponding to 69 of Figure 2d, it is desirable that light shall not fall upon the camera tube face until after completion of the sweeping of the preceding stored images, as is the case at the time corresponding to 1'! in Figure 2d.

The position of the advancing edge of the red filter section 81 at a time corresponding to 11 of Figure 2d may be approximately as indicated by a in Figure 3. By the time scanning of the red image begins and at a time corresponding .to H in Figure 2d, the advancing edge of the red color section 8'! will have reached position b. Figure 3 is drawn to show the position of the filter at the time scanning of the red image begins and at a time corresponding to 7 I in Figure 2d. The advance edge of the red section 8'! thereafter progresses downward across the image area 99 approximately equally ahead of the scanning line process. Scanning therefore may be made to occur somewhat ahead of the shadow of the spoke.

As an alternate procedure, a light transmitting color section of the filter may be caused to travel across the image area altogether ahead of the scanning process, so that the scanning takes place in the shadow of the spoke.

The width of the light transmitting color filter sections 85, 81, and 89 and their relationship to the scanning process will depend on numerous factors. Among these are the storage capabilities of the camera tube, the type of scanning, whether it be interlaced scanning or not, the sharpness or size of the scanning spot, the sensitivity of the tube, the brightness of the image falling on the camera tube, the extent to which secondary emission from scanning lines or areas creates electrical uniformity over the entire camera tube sensitive surface, and the permissible degree of color degradation resulting from minor remaining residual electrical images on the camera tube sensitive surface.

Having thus described the invention, what is claimed is:

1. In a television system having a camera tube with a photo-sensitive surface and an electron beam for scanning said surface, a method for removing electrical non-uniformity from said photo-sensitive surface during the interval between each successive field scanning comprising the steps of increasing the intensity of said beam during said interval, broadening said electron beam during said interval, sweeping said photosensitive surface with said broadened beam during said interval, and blocking the signal output of said photo-sensitive surface during said interval.

2. In a television system having a camera tube with a photo-sensitive surface and an electron beam for scanning said surface, a method for removing electrical non-uniformity from said photo-sensitive surface before each successive scanning comprising the steps of actuating an electrical circuit during the time interval between successive scannings to derive from said circuit a signal to increase the intensity of said electron beam during said interval, broaden the area of impact of said electron beam on said photosensitive surface during said interval, cause said electron beam to sweep the total area of said photo-sensitive surface during said interval, and block the signal output of said photo-sensitive surface during said interval.

3. In a television system having a camera tube with a photo-sensitive surface and an electron beam and a deflection signal generator to cause said electron beam to scan said photo-sensitive surface, a method for removing electrical nonuniformity from said photo-sensitive surface before each successive field scanning comprising the steps of deriving a signal from said deflection signal generator to actuate an electrical circuit during the time interval between successive field scannings, and to derive from said circuit a signal to increase the intensity of said electron beam during said interval, broaden the area of impact of said electron beam on said photo-sensitive surface during said interval, cause said electron beam to sweep the total area of said photo-sensi tive surface during said interval, and block the signal output of said photo-sensitive surface during said interval.

4. In a television system having a camera tube with a photo-sensitive surface and an electron beam, a deflection signal generator to cause said beam to scan said photo-sensitive surface, and an amplifier for said camera tube, a method for re moving electrical non-uniformity from said photo-sensitive surface before the time interval between each successive scanning traverse of the total photo-sensitive surface dimensions comprising the steps of deriving from said deflection signal generator a signal to actuate an electrical circuit during the time interval between successive scanning traverse of the total photo-sensitive surface dimensions and to derive from said circuit a signal to increase the intensity of said electron beam during said interval, broaden the area of said electron beam on said photo-sensitive surface during said interval, cause said electron beam to sweep the total area of said photosensitive surface during said interval, and block the outputof said amplifier during said interval;

5. In a television system having a camera tube with an image surface and an electron beam, and a deflection signal generator to cause said electron beam to scan said image surface, a method for removing any electrical non-uniformity from the total image surface before each successive scanning comprising the steps of deriving from said deflection signal generator a signal to actuate an electrical circuit during the time interval between successive scannings and to derive from said circuit a signal to increase the intensity of said electron beam during said interval, broaden the area of impact of said electron beam on said image surface during said interval, actuate a second deflection signal generator to cause said electron beam to sweep the total area of said image surface during said interval and block the signal output of said image surface during said interval.

6. In a television system having a camera tube with a photosensitive surface and an electron beam for scanning said surface, a field frequency generator and a line frequency generator to provide deflection voltages for said electron beam, a method for removing electrical non-uniformity from said photo-sensitive surface before each successive scanning comprising the steps of deriving from said field frequency generator a signal to actuate an electrical circuit during the time interval between successive scannings and to derive from said circuit a signal to increase the intensity of said electron beam during said interval, broaden the area of impact of said electron beam on said photo-sensitive surface during said interval, actuate a multi-field frequency generator and a multi-line frequency generator to cause said electron beam to swee the total area of said photo-sensitive surface during said interval, and block the signal output of said photo-sensitive surface during said interval.

7. In a television system having a camera tube with a photo-sensitive surface and an elzctron beam, a field frequency generator, and a line frequency generator for causing said beam to scan said photo-sensitivesurface, and an amplifier for said camera tube, a method for removing electrical non-uniformity from said photo-sensitive surface during the interval between each successive scanning comprising the steps of deriving from said field frequency generator a signal to increase the intensity of said electron beam during said interval, broaden the area of impact of said electron beam on said photo-sensitive surface during said interval, block the signal from said field frequency generator, line frequency generator, and amplifier, and activate a field frequency generator and a multi-line frequency generator to cause said electron beam to sweep the total area of said hoto-sensitive surface during said interval.

8. In a color television system having a camera tube with a photo-sensitive surface adapted to receive an image of an object, an electron beam for scanning said surface and a mobile color filter positioned adjacent said camera tube and comprising a plurality of color sections separated by opaque sections, a method for removing electrical non-uniformity from said photo-sensitive surface during the interval between each successive scanning comprising the steps of increasing the intensity of said beam during said interval, sweeping said photo-sensitive surface with said broadened beam during said interval, blocking the signal output of said photo-sensitive surface during said interval, and positioning during said interval one of said opaque sections between said photo-sensitive surface and the position of said object.

9. In a color television system having a camera tube with a photo-sensitive surface adapted to receive an image of an object, an electron beam for scanning said surface and a mobile color filter positioned adjacent said camera tube and comprising a plurality of color sections separated by opaque sections, a method for removing electrical non-uniformity from said photo-sensitive surface during the interval between each successive scanning comprising the steps of increasing the intensity of said beam during said interval, sweeping said photo-sensitive surface with said broadened beam during said interval, blocking the signal output of said photo-sensitive surface during said interval, and positioning one of said color sections between said photo-sensitive surface and the position of said object only during a time period other than during said interval.

i=3. In a color television system having a camera tube with photo-sensitive surface adapted to receive an image of an object, an electron beam for scanning said surface and a mobile color filter positioned adjacent said camera tube and comprising a plurality of color sections separated by opaque sections, a method for removing electrical nonuniformity from said photo-sensitive surface during the interval between each successive scanning comprising the steps of increasing the intensity of said beam during said interval, sweeping said photo-sensitive surface with said broadened beam during said interval, blocking the signal output of said photo-sensitive surface during said interval, and positioning one of said color sections between said photo-:sensitive surface and the position of said object only during the period of the time occupied by said scannings.

11. In a color television system having a camera tube with a photo-sensitive surface adapted to receive an image of. an object, an electron beam for scanning said surface and a mobile color filter positioned adjacent said camera tube and comprising a plurality .of color sections separated by opaque sections, said color sections being relatively small with respect to said opaque sections, a method for removing electrical non-uniformity from said photo-sensitive surface during the interval between each successive scanning comprising the steps of increasing the intensity of said beam during said interval, broadening said electron beam during said interval, sweeping said photo-sensitive surface with said broadened beam during said interval, blocking the signal output of said photo-sensitive surface during said interval, and positioning during said interval one of said opaque sections between said photo-sensitive surface and the position of said object.

12. In a television system containing a camera tube having a light sensitive electrode, an electron beam adapted to scan said electrode, an intensity control electrode, a focusing electrode, and deflection electrodes for said electron beam, an amplifier for said camera tube, a system for the removal of an electrical non-uniformit from said light sensitive electrode prior to each successive field scanning comprising in combination a circuit actuated during the interval between successive field sca'nnings and connected to said intensity control electrode to increase the intensity of said electron beam during said interval, a circuit connected to said focusing electrode to broaden said electron beam during said interval, a circuit connected to said deflection electrodes to cause said broadened electron beam to sweep said light sensitive electrode, and a circuit connected to said amplifier to block said amplifier during said interval.

13'. In a television system containing a camera tube having an image electrode, an electron beam adapted to scan said electrode, an intensity control electrode, a focusing electrode, and deflection means for said beam, an amplifier for said camera tube, a field frequency generator and a line frequency generator to roduce deflection signals for said electron beam, a system for the removal of any electrical non-uniformity from said electrode prior to each total scanning of both dimensions of said electrode comprising in combination a circuit connected to said field frequency generator to derive therefrom a signal potential during the interval between said successive scannings, a connection between said circuit and said intensity control electrode, focusing electrode, deflection means and said amplifier to increase the intensity of said electron-beam, broaden said beam to cause said electron beam to sweep said light sensitive electrode during said interval and to block'said amplifier during said interval.

14. In a television system containing a camera tube having a light sensitive electrode, an electron beam adapted to scan said electrode, an intensity control electrode, a focusing electrode, and

deflection electrodesfor said beam, an amplifierfor said camera tube, a field frequency generator, and a line frequency generator to produce deflection signals for said electron beam, a system for the removal of any electrical non-uniformityfrom said light sensitive electrode prior to each scanning comprising in combination a multi-field frequenc generator, a multi-line frequency generator, means connected to said field frequency generator to derive therefrom a signal to increase the intensity of said electron beam, broaden said electron beam and. to cause said multL-field frequency generator and said multi-line fre quency generator to produce a deflection signal for said deflection electrodes and timed to cause said electron beam to sweep said light sensitive electrode during the interval between successive scannings.

15. In a color television system containing a camera tube having a light sensitive electrode, an electron beam adapted to scan said electrode, an intensity control electrode, a focusing electrode, and deflection electrodes for said electron beam, a system for the removal of any electrical nonuniformity from said light sensitive electrode prior to each different color scanning comprising in combination a circuit actuated during the interval between successive different color scannings and connected to said intensity control electrode, focusing electrode, and deflection electrodes to cause said electron beam to sweep said light sensitive electrode during said time interval between successive different color scannings, and a mobile color filter positioned adjacent said camera tube and comprising a plurality of color sections separated by opaque sections, said color sections being relativel small with respect to said opaque sections.

1.6. In a color television system containing a camera tube having a light sensitive electrode,

an electron beam adapted to scan said electrode, an intensity control electrode, a focusing electrode, and deflection electrodes for said electron beam, a system for the removal of any electrical non-uniformity from said light sensitive electrode prior to each scanning comprising in combination a circuit actuated during the interval between successive scannings and connected to said intensity control electrode, focusing electrode, and deflection electrodes to cause said elecralit-y of color sections separated by opaque sections, said color sections being relatively small with respect to said opaque sections, and said mobile color filter adapted to present one of said opaque sections to opticall block out said electrode during said interval.

17. In a color television system containing a camera tube having a light sensitive electrode, an electron beam adapted to scan said electrode, an intensity control electrode, a focusing electrode, and deflection electrodes for said electron beam, a system for the removal of any electrical non-uniformity from; said light sensitive electrode prior to each scanning comprising in combination a circuit actuated during the interval between successive scannings and connected to said intensity control electrode, focusing elec trode, and deflection electrodes to cause said, electron beam to sweep-said light sensitive electrode during said time interval between successive scannings, and a, mobile color filter posi- 13 tioned adjacent said camera tube and comprising a plurality of color sections separated by opaque sections, said color sections being relatively small with respect to said opaque sections, said mobile color filter adapted to present one of said color sections only to the optical path of said electrode during said interval.

18. A color television system comprising in combination a cathode ray scanning tube having an output circuit and having a control electrode, m

a source of bias for said control electrode, a cathode ray focussing electrode for said cathode ray tube, a source of potential for said focussing electrode, a signal amplifier connected to said output circuit, means for changing the bias on said control electrode in a positive direction, means for changing the potential of said source of potential for said focussing electrode, means for blocking the transmission of signals through said amplifier, and a keying circuit connected to said bias changing means, said potential changing means and said blocking means for causing each of said means to operate only during the time interval between successive field scannings of said cathode ray tube.

ALFRED N. GOLDSMITH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,312,792 Bamford Mar. 2, 1943 2,413,075 Schade Dec. 24, 1946 2,435,963 Goldmark Feb. 17, 1948

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